An optical senor described in, for example, JP-A-11-72354 has been known as this kind of conventional optical sensor. The general outline of the optical senor described in JP-A-11-72354 will be described with reference to FIG. 14 to FIG. 16B.
As shown in FIG. 14, this optical sensor is constructed of a rectangular sensor housing 110 and an exterior filter 150 formed of, for example, transparent synthetic resin and fixed on the top of the sensor housing 110. An internal structure when the inside of this exterior filter 150 is viewed from the direction of a plane is shown in FIG. 15.
As shown in FIG. 15, this optical sensor is basically constructed of: a light receiving device 20 mounted in the center of the top surface of the sensor housing 110 (refer to FIG. 14) and for outputting an electric signal responsive to the amount of light received; and a light intercepting plate 140 for intercepting light, which is transmitted by the exterior filter 150 and is incident on the light receiving device 20, from above the light receiving device 20 to thereby adjust the amount of light incident on the light receiving device 20. In the light intercepting plate 140 of them, a slit 142a, 142b, 142c whose width is expanded stepwise is formed in a portion that intercepts light incident on the receiving surface of the light receiving device 20. The light intercepting plate 140 has an arm 144a extended from a portion, where these slit 142a to 142c is formed, to the left in the drawing and having a rotary shaft 141 on its tip. Moreover, the light intercepting plate 140 has an arm 144b which is extended from a portion where the slit 142a to 142c is formed to the right in the drawing and whose tip is sandwiched by a protrusion 150 formed on the inside wall of the exterior filter 150.
When the amount of light detected by the light receiving device 20 is adjusted, that is, when sensitivity is adjusted in this optical sensor, first, the exterior filter 150 is rotated, for example, 15 degrees clockwise. At this time, as shown in FIG. 16A and described above, the arm 144b of the light intercepting plate 140 is sandwiched by the protrusion 150a and hence the light intercepting plate 140 is also rotated 15 degrees around the rotary shaft 141 along with the rotation of the exterior filter 150. Hence, at this time, the light intercepting plate 140 is changed from a state where the light intercepting plate 140 having the slit width 142b shown in FIG. 15 intercepts light incident on the light receiving surface of the light receiving device 20 to a state where the light intercepting plate 140 having the slit width 142a intercepts light incident on the light receiving surface of the light receiving device 20, thereby a width passing the light incident on the light receiving surface of the light receiving device 20 is relatively narrowed. That is, the amount of light detected by the light receiving device 20 is made smaller than that before the rotation of the exterior filter 150, which results in decreasing sensitivity as the optical sensor. In contrast to this, when the exterior filter 150 is rotated 15 degrees counterclockwise, the light intercepting plate 140 is changed from a state where the light intercepting plate 140 having the slit width 142b shown in FIG. 15 intercepts light incident on the light receiving surface of the light receiving device 20 to a state where the light intercepting plate 140 having the slit width 142c intercepts light incident on the light receiving surface of the light receiving device 20, thereby a width passing the light incident on the light receiving surface of the light receiving device 20 is relatively expanded. That is, the amount of light detected by the light receiving device 20 is made larger than that before the rotation of the exterior filter 150, which results in increasing the sensitivity as the optical sensor.
In this manner, according to the above-mentioned conventional optical sensor, by rotating the exterior filter 150 clockwise or counterclockwise, the amount of light incident on the light receiving surface of the light receiving device 20, that is, the sensitivity of the optical sensor can be adjusted. However, although the total range of rotation in the clockwise and counterclockwise directions of the exterior filter 150 is as narrow as 30 degrees at a maximum as described above, the range of adjustment of the sensitivity of the optical sensor is wide. Hence, the degree of change in the sensitivity of the optical sensor with respect to the amount of rotation of the exterior filter 150 becomes large as a natural result.
Hence, in the case where such optical sensor is mounted in a vehicle, when the relative angle of the exterior filter 150 is changed even a little by the vibrations of the vehicle or the like, the sensitivity of the optical sensor may be excessively changed.
Moreover, even when the user rotates the exterior filter 150 a little at the time of setting sensitivity, the sensitivity of the optical sensor is changed by a large amount. Hence, it is difficult for the user to make the fine setting of sensitivity of the optical sensor.